1. Field of the Invention
The present invention relates to a separating apparatus for separating impurity from powder developer (referred to as "toner" hereinafter) in order to reuse the used toner for image formation used with an image forming apparatus such as an electrophotographic copying machine, an electrophotographic printer and the like for forming an image on a recording medium by using the toner, and an image forming apparatus utilizing such a separating apparatus.
2. Related Background
In conventional image forming apparatuses of this kind, it is common to collect toner removed from an electrophotographic photosensitive member by a cleaner after a toner image was formed on a recording medium. However, an image forming apparatus has been proposed wherein the collected toner is returned to a developing means for use in the image formation to achieve effective use of the toner.
By the way, the toner collected in the cleaner includes various foreign matter such as paper powder generated from the recording medium, dust, aggregated toner particles and the like mixed with the toner. If the collected toner is returned to the developing means as it is, it is impossible to obtain a good image.
To eliminate such a problem, regarding magnetic toner, involves taking advantage of the fact that the foreign matter mixed with the toner is substantially non-magnetic. That is to say, by generating a magnetic field in the vicinity of a mesh filter, the toner is forcibly passed through the filter, so that the foreign matter which was not passed through the filter is separated from the toner and then is collected (refer to, for example, Japanese Patent Publication No. 2-11913 filed on Oct. 30, 1980 and published on Mar. 16, 1990).
On the other hand, the inventors have proposed a technique in which magnetic field generating members are arranged above and below a mesh filter and the collected toner is supplied from a cleaner to a lower magnetic field so that, after the toner is absorbed to the lower magnetic field generating member, the toner alone is forcibly transferred to an upper stronger magnetic field through the mesh filter, thereby separating the foreign matter from the toner, which separated foreign matter is in turn collected (refer to U.S. Ser. Nos. 188,838, 188,883, 266,496 and 266,452).
According to the inventions described in the above U.S. Patent Application Specifications, when magnetic toner is used as toner, the foreign matters can be removed from the magnetic toner effectively, and, even when the magnetic toner, used once in the image formation, is used again in other image formation, a good image can be obtained.
The present invention relates to further improvement in the aforementioned inventions.